MkIIC+ Preamp clipping distortion, troubleshooting tips?

[rarebitusa]

Hi,

Hoping to get some technical input here. I've got a MkIIC+ HR and trying to troubleshoot a preamp clipping distortion problem. The setup is

amp -> 4 ohm Captor load -> AI

For those familiar with the Two Notes Captor, both the line out (dry) and DI with no speakersim enabled, produce the same results. Without a cab simulator I understand you'll get additional amp fizz, but this "clipping dist" is on top of the expected amp fizz. I have a Mk V and have done direct comparison and this "clip dist" is only on the C. With a cab and the Captor's -20db attn, it pretty much gets filtered out, but with direct recording and monitoring on an interface it's there, more distinct on Ch 1. BB member Thaymz sent me some clips of his C+ with a Captor out for comparison and it's obvious mine has issues

So far have verified

* Power section is clean, no audible "clip dist" with an effects return test (gtr + clean boost pedal)
* Captor load and interface are clean, levels are correct using effects return test and also Mk V
* using the effects send as the monitor with ch 1, rolled V1 and V2 with no real change in "clip dist"
* settings Ch 1, V1 - 6, T - 7, B - 3, M - 2, no pulls. No EQ pedal in loop.

Here's a link, this was done thru the complete amp, with a P-90 LP. Switching over to a HB based JP6 with more output signal, it was even more noticeable. Planning to do an updated clip, from the effects send with HBs, since it is more audible with that setup

https://youtu.be/hmC-Sj9JFfA

But in the meantime any input, links to look at would be welcomed. Thanks in advance.

 

[rarebitusa]

Here's a follow-up to this saga... decided to take it up to Mesa. Mike B spent a good deal of time with it and then we hung for a long while when I picked it up. The root of the problem is the power section was clipping, and that was very dependent on the load it was seeing. The solution is to find a "good" impedance match and to play around with different combinations of amp outputs to loads and trust your ears. It's certainly not liking the 4 ohm Captor load I was using, especially on the 4 ohm / 60W setting. We played thru a number of cabs there that sounded amazing, so thankfully there is nothing fundamentally wrong with it and I can move forward.

Can't say enough about Mike B, Rich Duvall and the folks at Mesa... Mike's just a great guy, taking the time to hang and educate me on a number of important "usage" points I just wasn't aware of.

 

[RR]

I don't know if what you experience is what I experience with my friend's Zinky amp.

I was playing a 4x12" with four 16 ohm Celetion Vintage 30s speakers wired in parallel - series for a 16 ohm load. We got this fizzy distortion. The setting on the Zinky was 16 ohm load.

So I wired the 4x12 all in parallel for a 4 ohms load. The fizzy distortion was gone and the usually pleasant distortion was back.

So I experminted since we had a pair of 8 ohms Vintage 30's. I wired in parallel, the usually pleasant distortion. I wired in series for 16 ohm load, the fizzy distortion.

Does this sounds like the phenomena you experienced?

 

[rarebitusa]

I don't know if what you experience is what I experience with my friend's Zinky amp.

I was playing a 4x12" with four 16 ohm Celetion Vintage 30s speakers wired in parallel - series for a 16 ohm load. We got this fizzy distortion. The setting on the Zinky was 16 ohm load.

So I wired the 4x12 all in parallel for a 4 ohms load. The fizzy distortion was gone and the usually pleasant distortion was back.

So I experminted since we had a pair of 8 ohms Vintage 30's. I wired in parallel, the usually pleasant distortion. I wired in series for 16 ohm load, the fizzy distortion.

Does this sounds like the phenomena you experienced?

Hi RR, yea sounds similar. You can tell something is not quite right, in your Zinky case that was on 16ohm. Were you hearing it perhaps more on clean settings?

In my case this clipping like distortion was much more pronounced on Ch 1 when using the Captor with 4ohm output and 60W, much less using 8 ohm and 100W. Mike mentioned that it was there even when he used a Mesa reactive load. Yesterday I was able to try an old Scholz resistive Power Soak and it sounded fine on both 4 and 8 ohm settings. I need to try a few more configurations now.